As aluminum alloy which is excellent in wear resistance, aluminum alloy which contains a large amount of Si is being widely used. Furthermore, it is also known to include Fe so as to improve the rigidity of aluminum alloy which contains a large amount of Si.
However, when producing aluminum alloy which contains a large amount of Si and Fe, the primary crystal Si and Al—Fe—Si-based compounds which precipitate in the process of cooling and solidification of the melt end up coarsening. Due to this, there was the problem that the strength, elongation, fatigue, and other mechanical properties fell and the workability ended up falling. In particular, Al—Fe—Si-based compounds are high in hardness and precipitate in needle shapes, so become obstacles in extrusion, rolling, and other secondary working.
To prevent coarsening of the primary crystal Si or Al—Fe—Si-based compounds when producing an aluminum alloy which contains a large amount of Si and Fe, various proposals have been made.
For example, PLT 1 proposes the method of adjusting the quantitative relationships of “Fe and Ni” and “Fe and Mn” to prevent coarse precipitates from forming and enabling precipitates to uniformly and finely disperse. Specifically, if adjusting the amounts of Ni, Fe, and Mn contained to Fe≦−0.25Ni+1.75 and further Mn≦0.6Fe in relationships, precipitation of easily coarsening Al3(Ni,Mn,Fe) is suppressed.
Further, PLT 2 adjusts the Si content to 1.7×Fe content+13 to 13.7 mass %, the Ti content to 0.05 to 0.07×Fe content+0.1 mass %, the Cr content to 0.1×Fe content+0.05 to 0.15 mass %, and the Mn content to 0.4 to 0.6×Fe content and treats the melt at the liquidus temperature or more by ultrasonic waves.
By treating the aluminum alloy melt at the liquidus temperature or more by ultrasonic vibration, the number of embryos of crystal nuclei of precipitates which form from the aluminum melt are increased to form a large number of fine crystal nuclei and cause precipitation of fine crystals. Further, by adjusting the ingredients and ranges of composition of the aluminum alloy melt as explained above, various types of precipitates are formed in a short time. Further, Al—Ti-based precipitates, Al—Cr-based precipitates, Al—Fe-based precipitates, and solitary Si are made to precipitate in that order and the Al—Fe-based precipitates are formed using the Al—Ti-based precipitates and Al—Cr-based precipitates as nuclei.